Cleanup: Pass std::string as const reference from content/

content/shell/browser/shell_mac.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/shell/browser/shell.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #import "base/mac/scoped_nsobject.h"
@@ skipping 285 matching lines @@
       break;
     case IDC_NAV_RELOAD:
       Reload();
       break;
     case IDC_NAV_STOP:
       Stop();
       break;
   }
 }
 
-void Shell::URLEntered(std::string url_string) {
+void Shell::URLEntered(const std::string& url_string) {
   if (!url_string.empty()) {
     GURL url(url_string);
     if (!url.has_scheme())
       url = GURL("http://" + url_string);
     LoadURL(url);
   }
 }
 
 void Shell::HandleKeyboardEvent(WebContents* source,
                                 const NativeWebKeyboardEvent& event) {
   if (event.skip_in_browser)
     return;
 
   // The event handling to get this strictly right is a tangle; cheat here a bit
   // by just letting the menus have a chance at it.
   if ([event.os_event type] == NSKeyDown) {
     if (([event.os_event modifierFlags] & NSCommandKeyMask) &&
         [[event.os_event characters] isEqual:@"l"]) {
       [window_ makeFirstResponder:url_edit_view_];
       return;
     }
 
     [[NSApp mainMenu] performKeyEquivalent:event.os_event];
   }
 }
 
 }  // namespace content